The system described herein relates generally to an improved cooling system. More specifically, the system relates to an improved cooling system for a generator and/or gearbox in a wind turbine.
Recently, wind turbines have received increased attention as environmentally safe and relatively inexpensive alternative energy sources. Wind turbines do not emit greenhouse gases (GHGs), and therefore, do not contribute to global warming. With the growing interest in wind generated electricity, considerable efforts have been made to develop wind turbines that are reliable and efficient.
Wind is usually considered to be a form of solar energy caused by uneven heating of the atmosphere by the sun, irregularities of the earth's surface, and rotation of the earth. Wind flow patterns are modified by the earth's terrain, bodies of water, and vegetation. The terms wind energy or wind power, describe the process by which the wind is used to rotate a shaft and subsequently generate mechanical power or electricity.
Typically, wind turbines are used to convert the kinetic energy in the wind into mechanical power. This mechanical power may be used for specific tasks (such as grinding grain or pumping water) or a generator may convert this mechanical power (i.e., the rotation of a shaft) into electricity. A wind turbine usually includes an aerodynamic mechanism (e.g., blades) for converting the movement of air into a mechanical motion (e.g., rotation), which is then converted with a generator into electrical power. Power output from the generator is proportional to the cube of the wind speed. As wind speed doubles, the capacity of wind generators increases almost eightfold.
The majority of commercially available wind turbines utilize geared drive trains to connect the turbine blades to the electrical generators. The wind turns the turbine blades, which spin a low speed shaft, which feeds into a gearbox having a higher speed output shaft. This higher speed output shaft connects to a generator which makes electricity. The geared drive aims to increase the velocity of the mechanical motion.
The industry standard drive train for large (e.g., >1 MW) wind turbines consists of discrete gearbox and generator units that are separately mounted to a mainframe (also commonly called a bedframe or bedplate). Power is transferred from the gearbox to the generator via a flexible “high-speed” shaft coupling. This arrangement forces the gearbox and generator to be physically distanced from each other, as well as, requires both the output shaft of the gearbox and the input shaft of the generator to be separately supported by gearbox bearings and generator bearings, respectively.
Heat exchangers are often used to dissipate the heat generated during operation of the generator and/or gearbox. Typically, a gearbox heat exchanger (e.g., oil to air) is connected to the gearbox and a generator heat exchanger (e.g., air to air) is mounted to a generator. These heat exchangers enable the generator (and/or gearbox) to be sealed from the environment, however, they are costly, heavy, and consume valuable power.
Conventional TEFC (totally-enclosed fan-cooled) and TEAO (totally-enclosed air-over) industrial motor cooling systems do not require heat exchangers to provide sealed systems, but arrangements blow cool inlet air from the motor non-drive end across external fins to the motor drive end. Both the inlet and exhausted air paths tend to be unducted, which would not be suitable for wind turbine applications where the nacelle is enclosed. Efficient and low-cost ducting of the external exhaust air path from the drive-end can be exceedingly difficult and would be especially challenging in wind turbine applications, and compact geared drive train configurations in particular, due to tight space and enclosure requirements enforced by the nacelle enclosure and bedplate.